Efficient production of nanofiber structures

ABSTRACT

Provided herein are electrospirming apparatuses and methods for efficient production of nanofiber structures.

RELATED APPLICATIONS

This application claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 62/754,183, filed Nov. 1, 2018, which is hereby incorporated by reference in its entirety.

BACKGROUND

Electrospinning is a fiber production method in which an electric force is applied to a polymer solution present at a spinning electrode. The application of the electric field pulls a charged thread of the solution from the spinning electrode towards a collecting electrode. This thread of polymer solution dries in flight, forming a fiber that is deposited on a substrate typically positioned at the collecting electrode. Depending upon the specific parameters applied to the electrospinning process, the produced fibers can have diameters ranging from a few nanometers up to several micrometers.

Electrospinning apparatuses are designed to adjust the position of the substrate and collector simultaneously. Most electrospinning studies utilize a grounded collector which serves both as the counter electrode and as the collecting substrate. This design makes it impossible to decouple the impacts of substrate distance vs. electric field strength, limiting the ability to independently test the effect of changes in these distances on electrospinning efficiency. Since the interelectrode gap needs to be maintained at a safe distance to prevent electrical discharge, especially at higher voltages, lower substrate distances have not been investigated as an independent variable.

SUMMARY

Provided herein are electrospinning apparatuses and methods of producing nanofiber structures with increased productivity (e.g., nanofiber mats).

In certain aspects, provided herein are electrospinning apparatuses that comprise: (a) a spinning electrode; (b) a substrate that is a first distance from the spinning electrode (the substrate distance); and (c) a collecting electrode that is a second distance from the spinning electrode (the interelectrode distance), wherein the substrate is positioned between the spinning electrode and the collecting electrode. In some embodiments, the ratio of the substrate distance to the interelectrode distance is less than 1 (e.g., no greater than 0.77).

In certain aspects, provided herein are electrospinning apparatuses comprising: (a) a spinning electrode; (b) a substrate that is a first distance from the spinning electrode (the substrate distance); and (c) a collecting electrode that is a second distance from the spinning electrode (the interelectrode distance), wherein the apparatus is configured such that the substrate distance and the interelectrode distance are separately adjustable and capable of being configured such that the ratio of the substrate distance to the interelectrode distance is less than 1.0 (e.g., no greater than 0.77).

In certain aspects, provided herein are methods of producing a nanofiber structure (e.g., a nanofiber mat) using an electrospinning apparatus provided herein. In some embodiments, the method comprises electrospinning a polymer solution from the spinning electrode of the apparatus provided herein onto its substrate.

Thus, in certain aspects, provided herein are methods for producing a nanofiber structure (e.g., a nanofiber mat) comprising electrospinning a polymer solution from a spinning electrode onto a substrate that is positioned between the spinning electrode and a collecting electrode, wherein the ratio of the substrate distance to the interelectrode distance is less than 1 (e.g., no greater than 0.77).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of certain conditions applied during the electrospinning experiments described in Example 1.

FIG. 2 is a graph depicting the relationship between substrate distance, electric field, basis weight and fiber diameter during exemplary electrospinning processes.

FIG. 3 shows a schematic depiction of certain conditions applied during in certain of the electrospinning experiments described in Example 2.

FIG. 4 shows a schematic depiction of conditions applied during electrospinning experiments described in Example 3 (Production unit). Runs 8 and 9 and well as 10 and 11 have identical experimental conditions. Each of these pairs have a differentiating line speed.

FIG. 5 shows a table summarizing the parameters applied and results obtained during Experiments 1-11 as set forth in Examples 1-3. “*- normalized by dividing the productivity by number of electrodes (i.e., N=8)”. The rows with bold letters are high productivity settings.

FIG. 6 shows the ability of certain embodiments disclosed herein to increase productivity while maintaining a product uniformity. Panel a depicts the increase in productivity per electrode (in g/m-min) achieved by decreasing the substrate distance while maintaining a constant electrode distance. Panel b shows that decreasing the substrate distance while maintaining a constant electrode distance does not adversely impact the count fiber mean diameter of the nanofiber mat produced. The hatched bar graph in panel b represents low-distance ratio. Higher productivity is augmented by combination of increasing the electric field and decreasing the distance ratio (d-s/d-ie).

FIG. 7 shows representative Scanning Electron Microscope (SEM) images of electrospun nanofiber generated at (a) standard and (b) high productivity settings using production equipment. The micrograph shows that comparable fiber structures were obtained at both settings.

DETAILED DESCRIPTION General

Electrospinning is a technique that can produce non-woven fibrous material with fiber diameters ranging from tens of nanometers to microns, a size range that is otherwise difficult to control by conventional non-woven fiber fabrication techniques. The quality and quantity of the fibers produced depend on several parameters. These parameters include molecular weight, molecular weight distribution and structure of the polymer; solution properties (i.e., viscosity, conductivity, and surface tension); electrical potential, flow rate, and concentration; distance between the spinning electrode and the substrate; environmental parameters (i.e., temperature, humidity, and air velocity in the chamber); motion and size of the collector; and needle gauge.

In certain aspects, provided herein are electrospinning apparatuses that can produce uniform nanofibers while improving process productivity without compromising the microstructure of the nanofiber mat by reducing the distance between spinning electrode and the substrate relative to the distance between the spinning electrode and the collecting electrode. Accordingly, the electrospinning apparatuses provided herein comprise (a) a spinning electrode; (b) a grounded substrate that is a first distance from the spinning electrode (the substrate distance); and (c) a collecting electrode that is a second distance from the spinning electrode (the interelectrode distance) wherein, the ratio of the substrate distance to the interelectrode distance is no greater than 1 (e.g., less than 0.86). In some embodiments, the apparatus is configured such that the substrate distance can be conveniently adjusted independent of the interelectrode distance (e.g., using a dial, lever and/or button). In certain aspects, provided herein are methods of making an electrospun structure, such as an electrospun mat, using an apparatus provided herein.

The productivity improvements provided by the methods and compositions disclosed herein have implications at the industrial production level. Certain embodiments of the methods and compositions provided herein can be used to increase amount of material being produced in an existing manufacturing line and, in doing so, decrease the production cost of a particular filter structure produced on that line. In some embodiments the methods and compositions provided herein can be used to make higher basis weight filter structures on an existing manufacturing line without increasing the production cost and without reducing the amount of material being produced.

Definitions

For convenience, certain terms employed in the specification, examples, and appended claims are collected here.

As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The term “about” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art. As used herein, “about” refers to an amount that is within 10% of a given value. In other words, these values include the stated value with a variation of 0-10% around the value (X±10%).

The terms “variation” and “coefficient of variation” are used interchangeably herein and refer to a standardized measure of dispersion of a probability distribution or frequency distribution. It is often expressed as a percentage and is defined as the ratio of the standard deviation to the mean.

The term “productivity” as used herein is a measure of the quantity of fiber produced per unit time per unit length of the spinning electrode (g/m-min). In certain embodiments, productivity is calculated as the product of the basis weight (g/m²) and line speed (m/min) and is directly related to the process economy.

The term “high productivity settings” as used herein refers to electrospinning apparatus settings in which the ratio of the substrate distance to the interelectrode distance is less than 0.88 (e.g., no greater than 0.75, 0.70, 0.65, 0.60. 0.55, 0.50, etc.). In some embodiments high productivity settings are applied in combination with the use of a high electric field (e.g., an electric field of at least 0.7 kV/mm).

The term “polymer” refers to a relatively high molecular weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit, the monomer (e.g., polyethylene, rubber, cellulose). Synthetic polymers are typically formed by addition or condensation polymerization of monomers. Polymers that are suitable for use in the nanofiber substrate layer of the invention include, but are not limited to, polyethersulfones, polysulfones, polyimides, polyvinylidene fluorides, polyethylene terephthalates, polybutylene terephthalates, polypropylene terephthalates, polypropylenes, polyethylenes, polyacrylonitriles, polyamides, and polyaramids.

The term “nanofiber” as used herein refers to fibers having a number average diameter or cross-section less than about 1000 nm, even less than about 800 nm, even between about 50 nm and 500 nm, and even between about 100 and 400 nm. The term diameter as used herein includes the greatest cross-section of non-round shapes.

The term “nonwoven” means a web including a multitude of randomly distributed fibers. The fibers generally can be bonded to each other or can be unbonded. The fibers can be staple fibers or continuous fibers. The fibers can comprise a single material or a multitude of materials, either as a combination of different fibers or as a combination of similar fibers each comprised of different materials.

Electrospinning Apparatus In general, an electrospinning apparatus consists of a spinning electrode that is connected to a high-voltage direct current power supply, a grounded collecting electrode, and optionally a needle for dispensing a polymer solution. Provided herein are apparatuses having a ratio of distance between the spinning electrode and the substrate (the substrate distance) to distance between the spinning electrode and the collecting electrode (the interelectrode distance) of less than 1. Also provided herein are apparatuses having an adjustable ratio of distance between the spinning electrode and the substrate (the substrate distance) to distance between the spinning electrode and the collecting electrode (the interelectrode distance).

In certain aspects, provided herein are electrospinning apparatuses that comprise: (a) a spinning electrode; (b) a substrate that is a first distance from the spinning electrode (the substrate distance); and (c) a collecting electrode that is a second distance from the spinning electrode (the interelectrode distance), wherein the substrate is positioned between the spinning electrode and the collecting electrode. In some embodiments, the ratio of the substrate distance to the interelectrode distance is less than 1 (e.g., less than 0.86).

In some embodiments the ratio of substrate distance to interelectrode distance is no more than 0.95, 0.90, 0.85, 0.80, 0.75, 0.70, 0.65, 0.60, 0.55, 0.50, 0.45, 0.40, or 0.35. In certain embodiments, the ratio of substrate distance to interelectrode distance is no greater than 0.86. In some embodiments, the ratio of substrate distance to interelectrode distance is at least 0.20, 0.25, or 0.30. In some embodiments, the ratio of the substrate distance to the interelectrode is from about 0.86 to about 0.3. In some embodiments, the ratio of the substrate distance to the interelectrode distance is between 0.80 and 0.70, 0.75 and 0.65, 0.70 and 0.60, 0.65 and 0.55, 0.60 and 0.50, 0.55 and 0.45, 0.50 and 0.40, 0.45 and 0.35, or 0.40 and 0.30. In some embodiments, the ratio of the substrate distance to the interelectrode distance is about 0.80, 0.75, 0.70, 0.65, 0.60, 0.55, 0.50, 0.45, 0.40, 0.35 or 0.30.

In some embodiments, the substrate distance is no more than about 200 mm, 190 mm, 180 mm, 170 mm, 160 mm, 150 mm, 140 mm, 130 mm, 120 mm, 110 mm, 100 mm, 90 mm, 80 mm, 70 mm, or 60 mm. In some embodiments, the substrate distance is at least about 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, or 70 mm. In some embodiments, the substrate distance is from about 140 mm to about 55 mm. In certain embodiments, the substrate distance is about 200 mm, 195 mm, 190 mm, 185 mm, 180 mm, 175 mm, 170 mm, 165 mm, 160 mm, 155 mm, 150 mm, 145 mm, 140 mm, 135 mm, 130 mm, 125 mm, 120 mm, 115 mm, 110 mm, 105 mm, 100 mm, 95 mm, 90 mm, 85 mm, 80 mm, 75 mm, 70 mm, 65 mm, 60 mm, or 55 mm.

In some embodiments, the interelectrode distance is such that the electrospinning apparatus maintains an electric field at least 0.2 kV/mm. In some embodiments, the interelectrode distance is such that the apparatus maintains an electric field of at least 0.2 kV/mm, 0.3 kV/mm, 0.4 kV/mm, 0.5 kV/mm, 0.6 kV/mm, or 0.7 kV/mm. In some embodiments, the interelectrode distance is such that the apparatus maintains an electric field of no more than 0.8 kV/mm, 0.70 kV/mm, or 0.6 kV/mm. In some embodiments, the interelectrode distance is such that the apparatus maintains an electric field of 0.2 kV/mm to 0.8 kV/mm. In some embodiments, the interelectrode distance is such that the electrospinning apparatus maintains an electric field of about 0.2 kV/mm, 0.25 kV/mm, 0.3 kV/mm, 0.35 kV/mm, 0.4 kV/mm, 0.45 kV/mm, 0.5 kV/mm, 0.55 kV/mm, 0.6 kV/mm, 0.65 kV/mm, 0.7 kV/mm, 0.75 kV/mm, or 0.8 kV/mm.

In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of at least 30 μm at a rate of at least 0.30 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of at least 30 μm at a rate of at least 0.35 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of at least 35 μm at a rate of at least 0.30 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of at least 35 μm at a rate of at least 0.35 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of 37 μm at a rate of 0.35 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of at least 15 μm at a line speed of at least 0.80 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of at least 15 μm at a line speed of at least 0.85 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of at least 15 μm at a rate of at least 0.90 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of at least 15 μm at a rate of at least 0.95 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of at least 15 μm at a rate of at least 1.0 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of at least 19 μm at a rate of at least 0.80 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of at least 19 μm at a rate of at least 0.85 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of at least 19 μm at a rate of at least 0.90 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of at least 19 μm at a rate of at least 0.95 m/min. In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of 19 μm at a rate of 0.98 m/min.

In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat (e.g., a nanofiber mat having a fiber diameter of no more than 200 nm) with a productivity of above at least 0.20 g/(m-min), above at least 0.21 g/(m-min), above at least 0.22 g/(m-min), above at least 0.23 g/(m-min), above at least 0.24 g/(m-min), above at least 0.25 g/(m-min), above at least 0.26 g/(m-min), above at least 0.27 g/(m-min), above at least 0.28 g/(m-min), above at least 0.29 g/(m-min), above at least 0.30 g/(m-min), above at least 0.31 g/(m-min), above at least 0.32 g/(m-min), or above at least 0.33 g/(m-min).

In some embodiments, the electrospinning apparatus is capable of generating a nanofiber mat having a fiber diameter variation of no more than 36%, no more than 29%, no more than 28%, no more than 27%, no more than 26%, no more than 25%, no more than 24%, no more than 23%, no more than 22%, no more than 21%, no more than 20%, no more than 19%, no more than 18%, no more than 17%,.

In certain aspects, provided herein are electrospinning apparatuses comprising: (a) a spinning electrode; (b) a substrate that is a first distance from the spinning electrode (the substrate distance); and (c) a collecting electrode that is a second distance from the spinning electrode (the interelectrode distance), wherein the apparatus is configured such that the substrate distance and the interelectrode distance are separately adjustable and capable of being configured such that the ratio of the substrate distance to the interelectrode distance is no greater than 1.0.

In some embodiments, the substrate distance can be adjusted without adjusting the interelectrode distance (e.g., using a knob, lever, motor or button). For example, in some embodiments the position of the substrate can be changed (e.g., using a knob, lever, motor or button) without changing the position of the spinning electrode or the collecting electrode. In some embodiments the position of the collecting electrode can be changed (e.g., using a knob, lever, motor or button) without changing the position of the spinning electrode or the substrate. In some embodiments, the position of the spinning electrode, substrate and/or collecting electrode can be independently adjusted remotely (e.g., using a motor controlled by an electronic input, such as computer or other electronic device). In some embodiments the position of the spinning electrode, substrate and/or collecting electrode can be adjusted manually without disassembling the apparatus (e.g., using a knob, lever, or button).

In some embodiments the substrate distance and the interelectrode distance are separately adjustable and capable of being configured such that the ratio of the substrate distance to the interelectrode distance is no more than 0.95, 0.90, 0.85, 0.80, 0.75, 0.70, 0.65, 0.60, 0.55, 0.50, 0.45, 0.40, or 0.35. In certain embodiments, the substrate distance and the interelectrode distance are separately adjustable and capable of being configured such that the ratio of the substrate distance to the interelectrode distance is no greater than 0.77. In some embodiments, the substrate distance and the interelectrode distance are separately adjustable and capable of being configured such that the ratio of the substrate distance to the interelectrode distance is at least 0.20, 0.25, or 0.30. In some embodiments, the substrate distance and the interelectrode distance are separately adjustable and capable of being configured such that the ratio of the substrate distance to the interelectrode distance is from about 0.77 to about 0.3. In some embodiments, the substrate distance and the interelectrode distance are separately adjustable and capable of being configured such that the ratio of the substrate distance to the interelectrode distance is between 0.80 and 0.70, 0.75 and 0.65, 0.70 and 0.60, 0.65 and 0.55, 0.60 and 0.50, 0.55 and 0.45, 0.50 and 0.40, 0.45 and 0.35, or 0.40 and 0.30. In some embodiments, the substrate distance and the interelectrode distance are separately adjustable and capable of being configured such that the ratio of the substrate distance to the interelectrode distance is about 0.80, 0.75, 0.70, 0.65, 0.60, 0.55, 0.50, 0.45, 0.40, 0.35 or 0.30.

In some embodiments, the substrate distance can be adjusted to be less than about 200 mm, 190 mm, 180 mm, 170 mm, 160 mm, 150 mm, 140 mm, 130 mm, 120 mm, 110 mm, 100 mm, 90 mm, 80 mm, 70 mm, or 60 mm. In some embodiments, the substrate distance can be adjusted to be at least about 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, or 70 mm. In some embodiments, the substrate distance can be adjusted to be from about 140 mm to about 55 mm. In certain embodiments, the substrate distance can be adjusted to be about 200 mm, 195 mm, 190 mm, 185 mm, 180 mm, 175 mm, 170 mm, 165 mm, 160 mm, 155 mm, 150 mm, 145 mm, 140 mm, 135 mm, 130 mm, 125 mm, 120 mm, 115 mm, 110 mm, 105 mm, 100 mm, 95 mm, 90 mm, 85 mm, 80 mm, 75 mm, 70 mm, 65 mm, 60 mm, or 55 mm.

In some embodiments, the interelectrode distance can be adjusted to be such that the electrospinning apparatus maintains an electric field at least 0.2 kV/mm. In some embodiments, the interelectrode distance can be adjusted to be such that the apparatus maintains an electric field of at least 0.2 kV/mm, 0.3 kV/mm, 0.4 kV/mm, 0.5 kV/mm, 0.6 kV/mm, or 0.7 kV/mm. In some embodiments, the interelectrode distance can be adjusted to be such that the apparatus maintains an electric field of no more than 0.8 kV/mm, 0.70 kV/mm, or 0.6 kV/mm. In some embodiments, the interelectrode distance can be adjusted to be such that the apparatus maintains an electric field of 0.2 kV/mm to 0.8 kV/mm. In some embodiments, the interelectrode distance can be adjusted to be such that the electrospinning apparatus maintains an electric field of about 0.2 kV/mm, 0.25 kV/mm, 0.3 kV/mm, 0.35 kV/mm, 0.4 kV/mm, 0.45 kV/mm, 0.5 kV/mm, 0.55 kV/mm, 0.6 kV/mm, 0.65 kV/mm, 0.7 kV/mm, 0.75 kV/mm, or 0.8 kV/mm.

In some embodiments, the substrate of the apparatuses provided herein can be formed from any material. In certain embodiments, the substrate is a nonwoven fiber substrate. In certain embodiments, the substrate is a non-porous film substrate or paper. In some embodiments, the substrate is a porous substrate.

In some embodiments, the spinning electrode of the apparatuses provided herein further comprise a nozzle. In some embodiments the spinning electrode is nozzleless. In some embodiments, the spinning electrode comprises a rotating roller or rotating drum or wire.

In some embodiments, the collecting electrode of the apparatuses provided herein comprise a conductive surface. In some embodiments, the collecting electrode is a flat plate, moving plate or belt, tube, wire, or rotating drum.

Methods of Producing Non-Woven Fiber Structures

Electrospinning is process of producing nanofibers from a mixture of polymers, for example, polymer solution or polymer melt. The process involves applying an electric potential to such a polymer solution or polymer melt. Certain details of the electrospinning process for making an electrospun nanofiber mat or membrane, including suitable apparatuses for performing the electrostatic spinning process, are described in International Patent Application Publications WO2005/024101, WO2006/131081, and WO2008/106903, each of which is incorporated herein by reference in its entirety.

During electrospinning process, fibers are generated from a spinning electrode by applying a high voltage to the electrodes and a polymer solution where fibers are charged or spun toward a collecting electrode and collected as a highly porous non-woven mat on a substrate between the electrodes.

Two methods to electrospinning are capillary and free-surface electrospinning. Needle electrospinning is typically set up where the spinning electrode is a metal syringe, which also dispenses the polymer solution via a syringe pump. Needle electrospinning set-ups are typically performed in custom lab scale or smaller commercially produced machines.

Needle-less electrospinning provides greater productivity of fiber mass per unit time and length of the spinning electrode and the ability to operate on a wider area and on moving basis to collect continuous roll stock of non-woven fiber mat membranes. Examples of commercial needle-less electrospinning equipment include ELMARCO, s.r.o. (Liberec, Czech Republic). ELMARCO electrospinning machines function with two types of dispensing of the polymer solution onto the spinning electrode. In certain embodiments, provided herein ELMARCO electrospinning machine NS 3S1000U is a pilot scale unit equipped with 1 to 3 wire spinning electrodes and can deposit nanofiber on a 1.0 m wide moving or stationary substrate. In certain embodiments, provided herein ELMARCO electrospinning machine NS 8S1600U is a production unit, equipped with 1 to 8 wire spinning electrodes and can deposit nanofiber on 1.6 m wide moving or stationary substrate.

In certain aspects, provided herein are methods of producing a non-woven fiber mat using the electrospinning apparatuses disclosed herein comprising an electrospinning a polymer solution from the spinning electrode of the electrospinning apparatus onto the substrate of the electrospinning apparatus, are also provided. In certain aspects, provided herein are methods of producing a nanofiber structure (e.g., a nanofiber mat) using an electrospinning apparatus provided herein. In some embodiments, the method comprises electrospinning a polymer solution from the spinning electrode of the apparatus provided herein onto its substrate.

Thus, in certain aspects, provided herein are methods for producing a nanofiber structure (e.g., a nanofiber mat) comprising electrospinning a polymer solution from a spinning electrode onto a substrate that is positioned between the spinning electrode and a collecting electrode, wherein the ratio the substrate distance to the interelectrode distance is less than 1.

In some embodiments of the methods provided herein, the ratio of substrate distance to interelectrode distance is no more than 0.95, 0.90, 0.85, 0.80, 0.75, 0.70, 0.65, 0.60, 0.55, 0.50, 0.45, 0.40, or 0.35. In certain embodiments, the ratio of substrate distance to interelectrode distance is no greater than 0.77. In some embodiments, the ratio of substrate distance to interelectrode distance is at least 0.20, 0.25, or 0.30. In some embodiments, the ratio of the substrate distance to the interelectrode is from about 0.77 to about 0.3. In some embodiments, the ratio of the substrate distance to the interelectrode distance is between 0.80 and 0.70, 0.75 and 0.65, 0.70 and 0.60, 0.65 and 0.55, 0.60 and 0.50, 0.55 and 0.45, 0.50 and 0.40, 0.45 and 0.35, or 0.40 and 0.30. In some embodiments, the ratio of the substrate distance to the interelectrode distance is about 0.80, 0.75, 0.70, 0.65, 0.60, 0.55, 0.50, 0.45, 0.40, 0.35 or 0.30.

In some embodiments of the methods provided herein, the substrate distance is no more than about 200 mm, 190 mm, 180 mm, 170 mm, 160 mm, 150 mm, 140 mm, 130 mm, 120 mm, 110 mm, 100 mm, 90 mm, 80 mm, 70 mm, or 60 mm. In some embodiments, the substrate distance is at least about 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, or 70 mm. In some embodiments, the substrate distance is from about 140 mm to about 55 mm. In certain embodiments, the substrate distance is about 200 mm, 195 mm, 190 mm, 185 mm, 180 mm, 175 mm, 170 mm, 165 mm, 160 mm, 155 mm, 150 mm, 145 mm, 140 mm, 135 mm, 130 mm, 125 mm, 120 mm, 115 mm, 110 mm, 105 mm, 100 mm, 95 mm, 90 mm, 85 mm, 80 mm, 75 mm, 70 mm, 65 mm, 60 mm, or 55 mm.

In some embodiments of the methods provided herein, the nanofibers are electrospun at a voltage of 10 kV to 500 kV, 50 kV to 450 kV, 100 kV to 400 kV, 150 kV to 350 kV, or 200 kV to 300 kV. In some embodiments of the methods provided herein, the nanofibers are electrospun at a voltage of 10 kV to 20 kV, 15 kV to 25 kV, 20 kV to 30 kV, 25 kV to 35 kV, 30 kV to 40 kV, 35 kV to 45 kV, 40 kV to 50 kV, 45 kV to 55 kV, 50 kV to 60 kV, 55 kV to 65 kV, 60 kV to 70 kV, 65 kV to 75 kV, 70 kV to 80 kV, 75 kV to 85 kV, 80 kV to 90 kV, 85 kV to 95 kV, 90 kV to 100 kV, 95 kV to 105 kV, 100 kV to 110 kV, 105 kV to 115 kV, 110 kV to 120 kV, 115 kV to 125 kV, 120 kV to 130 kV, 125 kV to 135 kV, 130 kV to 140 kV, 135 kV to 145 kV, 140 kV to 150 kV, 145 kV to 155 kV, 150 kV to 160 kV, 155 kV to 165 kV, 160 kV to 170 kV, 165 kV to 175 kV, 170 kV to 180 kV, 175 kV to 185 kV, 180 kV to 190 kV, 185 kV to 195 kV, 190 kV to 200 kV, 195 kV to 205 kV, 200 kV to 210 kV, 205 kV to 215 kV, 210 kV to 220 kV, 215 kV to 225 kV, 220 kV to 230 kV, 225 kV to 235 kV, 230 kV to 240 kV, 235 kV to 245 kV, 240 kV to 250 kV, 245 kV to 255 kV, 250 kV to 260 kV, 255 kV to 265 kV, 260 kV to 270 kV, 265 kV to 275 kV, 270 kV to 280 kV, 275 kV to 285 kV, 280 kV to 290 kV, 285 kV to 295 kV, 290 kV to 300 kV, 295 kV to 305 kV, 300 kV to 310 kV, 305 kV to 315 kV, 310 kV to 320 kV, 315 kV to 325 kV, 320 kV to 330 kV, 325 kV to 335 kV, 330 kV to 340 kV, 335 kV to 345 kV, 340 kV to 350 kV, 345 kV to 355 kV, 350 kV to 360 kV, 355 kV to 365 kV, 360 kV to 370 kV, 365 kV to 375 kV, 370 kV to 380 kV, 375 kV to 385 kV, 380 kV to 390 kV, 385 kV to 395 kV, 390 kV to 400 kV, 395 kV to 405 kV, 400 kV to 410 kV, 405 kV to 415 kV, 410 kV to 420 kV, 415 kV to 425 kV, 420 kV to 430 kV, 425 kV to 435 kV, 430 kV to 440 kV, 435 kV to 445 kV, 440 kV to 450 kV, 445 kV to 455 kV, 450 kV to 460 kV, 455 kV to 465 kV, 460 kV to 470 kV, 465 kV to 475 kV, 470 kV to 480 kV, 475 kV to 485 kV, 480 kV to 490 kV, 485 kV to 495 kV, or 490 kV to 500 kV.

In some embodiments, the interelectrode distance is such that the electrospinning apparatus maintains an electric field at least 0.2 kV/mm. In some embodiments, the interelectrode distance is such that the apparatus maintains an electric field of at least 0.2 kV/mm, 0.3 kV/mm, 0.4 kV/mm, 0.5 kV/mm, 0.6 kV/mm, or 0.7 kV/mm. In some embodiments, the interelectrode distance is such that the apparatus maintains an electric field of no more than 0.8 kV/mm, 0.70 kV/mm, or 0.6 kV/mm. In some embodiments, the interelectrode distance is such that the apparatus maintains an electric field of 0.2 kV/mm to 0.8 kV/mm. In some embodiments, the interelectrode distance is such that the electrospinning apparatus maintains an electric field of about 0.2 kV/mm, 0.25 kV/mm, 0.3 kV/mm, 0.35 kV/mm, 0.4 kV/mm, 0.45 kV/mm, 0.5 kV/mm, 0.55 kV/mm, 0.6 kV/mm, 0.65 kV/mm, 0.7 kV/mm, 0.75 kV/mm, or 0.8 kV/mm.

In some embodiments, the polymer solution comprises a polymer or a polymer blend. For example, in some embodiments the polymer or polymer blend is selected from nylon-6, nylon-46, nylon-66, polyaramids, polyurethane (PU), polybenzimidazole, polycarbonate, polyacrylonitrile, polyvinyl alcohol, polylactic acid (PLA), polyethylene-co-vinyl acetate (PEVA), PEVA/PLA, polymethylmethacrylate (PMMA), PMMA/tetrahydroperfluorooctylacrylate (TAN), polyethylene oxide (PEO), collagen-PEO, polystyrene (PS), polyaniline (PANI)/PEO, PANI/PS, polyvinylcarbazole, polyethylene terephthalate (PET), polyacrylic acid-polypyrene methanol (PAA-PM), polyamide (PA), silk/PEO, polyvinylphenol (PVP), polyvinylchloride (PVC), cellulose acetate (CA), PAA-PM/PU, polyvinyl alcohol (PVA)/silica, polyacrylamide (PAAm), poly(lactic-co-glycolic acid) (PLGA), polycarprolactone (PCL), poly(2-hydroxyethyl methacrylate) (HEMA), poly(vinylidene difluoride) (PVDF), PVDF/PMMA, polyether imide (PEI), polyethylene glycol (PEG), poy(ferrocenyldimethylsilane) (PFDMS), Nylon6/montmorillonite (Mt), poly(ethylene-co-vinyl alcohol), polyacrylnitrile (PAN)/TiO2, polycaprolactone (PCL)/metal, polyvinyl porrolidone, polymetha-phenylene isophthalamide, polyethylene (PE), polypropylene (PP), nylon-12, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), polyvinyl butyral (PVB), PET/PEN, or a blend thereof.

In some embodiments, the substrate of the apparatuses provided herein can be formed from any material. In certain embodiments, the substrate is a nonwoven fiber substrate. In certain embodiments, the substrate is a non-porous film substrate. In some embodiments, the substrate is a porous substrate. In some embodiments, the substrate is a paper. In some embodiments, the substrate is grounded.

In some embodiments, the spinning electrode of the apparatuses provided herein further comprise a nozzle. In some embodiments the spinning electrode is nozzleless. In some embodiments, the spinning electrode comprises a rotating roller or rotating drum or wire.

In some embodiments, the collecting electrode of the apparatuses provided herein comprise a conductive surface. In some embodiments, the collecting electrode is a flat plate, moving plate, tube, wire, or rotating drum.

In some embodiments, the nanofiber mat is generated at a line speed of 0.03 m/min to 1 m/min. In some embodiments, the line speed is at least about 0.03 m/min, 0.04 m/min, 0.05 m/min, 0.06 m/min, 0.07 m/min, 0.08 m/min, 0.09 m/min, 0.10 m/min, 0.11 m/min, 0.12 m/min, 0.13 m/min, 0.14 m/min, 0.15 m/min, 0.16 m/min, 0.17 m/min, 0.18 m/min, 0.19 m/min, 0.20 m/min, 0.21 m/min, 0.22 m/min,. 0.23 m/min, 0.24 m/min, 0.25 m/min, 0.26 m/min, 0.27 m/min, 0.28 m/min, 0.29 m/min, 0.30 m/min, 0.31 m/min, 0.32 m/min, 0.33 m/min, 0.34 m/min, 0.35 m/min, 0.36 m/min, 0.37 m/min, 0.38 m/min, 0.39 m/min, 0.40 m/min, 0.41 m/min, 0.42 m/min, 0.43 m/min, 0.44 m/min, 0.45 m/min, 0.46 m/min, 0.47 m/min, 0.48 m/min, 0.49 m/min, 0.50 m/min, 0.51 m/min, 0.52 m/min, 0.53 m/min, 0.54 m/min, 0.55 m/min, 0.56 m/min, 0.57 m/min, 0.58 m/min, 0.59 m/min, 0.60 m/min, 0.61 m/min, 0.62 m/min, 0.63 m/min, 0.64 m/min, 0.65 m/min, 0.66 m/min, 0.67 m/min, 0.68 m/min, 0.69 m/min, 0.70 m/min, 0.71 m/min, 0.72 m/min, 0.73 m/min, 0.74 m/min, 0.75 m/min, 0.76 m/min, 0.77 m/min, 0.78 m/min, 0.79 m/min, 0.80 m/min, 0.81 m/min, 0.82 m/min, 0.83 m/min, 0.84 m/min, 0.85 m/min, 0.86 m/min, 0.87 m/min, 0.88 m/min, 0.89 m/min, 0.90 m/min, 0.91 m/min, 0.92 m/min, 0.93 m/min, 0.94 m/min, 0.95 m/min, 0.96 m/min, 0.97 m/min, 0.98 m/min, 0.99 m/min, or 1.00 m/min. In certain embodiments, the line speed is about 0.03 m/min, 0.04 m/min, 0.05 m/min, 0.06 m/min, 0.07 m/min, 0.08 m/min, 0.09 m/min, 0.10 m/min, 0.11 m/min, 0.12 m/min, 0.13 m/min, 0.14 m/min, 0.15 m/min, 0.16 m/min, 0.17 m/min, 0.18 m/min, 0.19 m/min, 0.20 m/min, 0.21 m/min, 0.22 m/min,. 0.23 m/min, 0.24 m/min, 0.25 m/min, 0.26 m/min, 0.27 m/min, 0.28 m/min, 0.29 m/min, 0.30 m/min, 0.31 m/min, 0.32 m/min, 0.33 m/min, 0.34 m/min, 0.35 m/min, 0.36 m/min, 0.37 m/min, 0.38 m/min, 0.39 m/min, 0.40 m/min, 0.41 m/min, 0.42 m/min, 0.43 m/min, 0.44 m/min, 0.45 m/min, 0.46 m/min, 0.47 m/min, 0.48 m/min, 0.49 m/min, 0.50 m/min, 0.51 m/min, 0.52 m/min, 0.53 m/min, 0.54 m/min, 0.55 m/min, 0.56 m/min, 0.57 m/min, 0.58 m/min, 0.59 m/min, 0.60 m/min, 0.61 m/min, 0.62 m/min, 0.63 m/min, 0.64 m/min, 0.65 m/min, 0.66 m/min, 0.67 m/min, 0.68 m/min, 0.69 m/min, 0.70 m/min, 0.71 m/min, 0.72 m/min, 0.73 m/min, 0.74 m/min, 0.75 m/min, 0.76 m/min, 0.77 m/min, 0.78 m/min, 0.79 m/min, 0.80 m/min, 0.81 m/min, 0.82 m/min, 0.83 m/min, 0.84 m/min, 0.85 m/min, 0.86 m/min, 0.87 m/min, 0.88 m/min, 0.89 m/min, 0.90 m/min, 0.91 m/min, 0.92 m/min, 0.93 m/min, 0.94 m/min, 0.95 m/min, 0.96 m/min, 0.97 m/min, 0.98 m/min, 0.99 m/min, or 1.00 m/min.

In some embodiments, the product of the method is a nanofiber mat. In some embodiments, the produced nanofiber mat has a thickness from about 1μm to about 500 μm. In some embodiments, the nanofiber mat has a thickness of at least 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 135 μm, 140 μm, 145 μm, 150 μm, 155 μm, 160 μm, 165 μm, 170 μm, 175 μm, 180 μm, 185 μm, 190 μm, 195 μm, 200 μm, 205 μm, 210 μm, 215 μm, 220 μm, 225 μm, 230 μm, 235 μm, 240 μm, 245 μm, 250 μm, 255 μm, 260 μm, 265 μm, 270 μm, 275 μm, 280 μm, 285 μm, 290 μm, 295 μm, 300 μm, 305 μm, 310 μm, 315 μm, 320 μm, 325 μm, 330 μm, 335 μm, 340 μm, 345 μm, 350 μm, 355 μm, 360 μm, 365 μm, 370 μm, 375 μm, 380 μm, 385 μm, 390 μm, 395 μm, 400 μm, 405 μm, 410 μm, 415 μm, 420 μm, 425 μm, 430 μm, 435 μm, 440 μm, 445 μm, 450 μm, 455 μm, 460 μm, 465 μm, 470 μm, 475 μm, 480 μm, 485 μm, 490 μm, 495 μm, or 500 μm. In some embodiments, the nanofiber mat has a thickness of about 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 135 μm, 140 μm, 145 μm, 150 μm, 155 μm, 160 μm, 165 μm, 170 μm, 175 μm, 180 μm, 185 μm, 190 μm, 195 μm, 200 μm, 205 μm, 210 μm, 215 μm, 220 μm, 225 μm, 230 μm, 235 μm, 240 μm, 245 μm, 250 μm, 255 μm, 260 μm, 265 μm, 270 μm, 275 μm, 280 μm, 285 μm, 290 μm, 295 μm, 300 μm, 305 μm, 310 μm, 315 μm, 320 μm, 325 μm, 330 μm, 335 μm, 340 μm, 345 μm, 350 μm, 355 μm, 360 μm, 365 μm, 370 μm, 375 μm, 380 μm, 385 μm, 390 μm, 395 μm, 400 μm, 405 μm, 410 μm, 415 μm, 420 μm, 425 μm, 430 μm, 435 μm, 440 μm, 445 μm, 450 μm, 455 μm, 460 μm, 465 μm, 470 μm, 475 μm, 480 μm, 485 μm, 490 μm, 495 μm, or 500 μm.

In some embodiments, the produced nanofiber structure (e.g., nanofiber mat) has an average fiber diameter from about 10 nm to about 1000 nm. The fiber diameter has a wide distribution ranging 16-36% CoV. In some embodiments, the average nanofiber diameter is no more than 1000 nm, 950 nm, 900 nm, 850 nm, 800 nm. 750 nm, 700 nm, 650 nm, 600 nm, 550 nm, 500 nm, 450 nm, 400 nm, 350 nm, 300 nm, 250 nm, 200 nm, 150 nm, 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, or 20 nm. In some embodiments, the average nanofiber diameter is 10 nm to 20 nm, 15 nm to 25 nm, 20 nm to 30 nm, 25 nm to 35 nm, 30 nm to 40 nm, 35 nm to 45 nm, 40 nm to 50 nm, 45 nm to 55 nm, 50 nm to 60 nm, 55 nm to 65 nm, 60 nm to 70 nm, 65 nm to 75 nm, 70 nm to 80 nm, 75 nm to 85 nm, 80 nm to 90 nm, 85 nm to 95 nm, 90 nm to 100 nm, 95 nm to 105 nm, 100 nm to 110 nm, 105 nm to 115 nm, 110 nm to 120 nm, 115 nm to 125 nm, 120 nm to 130 nm, 125 nm to 135 nm, 130 nm to 140 nm, 135 nm to 145 nm, 140 nm to 150 nm, 145 nm to 155 nm, 150 nm to 160 nm, 155 nm to 165 nm, 160 nm to 170 nm, 165 nm to 175 nm, 170 nm to 180 nm, 175 nm to 185 nm, 180 nm to 190 nm, 185 nm to 195 nm, 190 nm to 200 nm, 195 nm to 205 nm, 200 nm to 210 nm, 205 nm to 215 nm, 210 nm to 220 nm, 215 nm to 225 nm, 220 nm to 230 nm, 225 nm to 235 nm, 230 nm to 240 nm, 235 nm to 245 nm, 240 nm to 250 nm, 245 nm to 255 nm, 250 nm to 260 nm, 255 nm to 265 nm, 260 nm to 270 nm, 265 nm to 275 nm, 270 nm to 280 nm, 275 nm to 285 nm, 280 nm to 290 nm, 285 nm to 295 nm, 290 nm to 300 nm, 295 nm to 305 nm, 300 nm to 310 nm, 305 nm to 315 nm, 310 nm to 320 nm, 315 nm to 325 nm, 320 nm to 330 nm, 325 nm to 335 nm, 330 nm to 340 nm, 335 nm to 345 nm, 340 nm to 350 nm, 345 nm to 355 nm, 350 nm to 360 nm, 355 nm to 365 nm, 360 nm to 370 nm, 365 nm to 375 nm, 370 nm to 380 nm, 375 nm to 385 nm, 380 nm to 390 nm, 385 nm to 395 nm, 390 nm to 400 nm, 395 nm to 405 nm, 400 nm to 410 nm, 405 nm to 415 nm, 410 nm to 420 nm, 415 nm to 425 nm, 420 nm to 430 nm, 425 nm to 435 nm, 430 nm to 440 nm, 435 nm to 445 nm, 440 nm to 450 nm, 445 nm to 455 nm, 450 nm to 460 nm, 455 nm to 465 nm, 460 nm to 470 nm, 465 nm to 475 nm, 470 nm to 480 nm, 475 nm to 485 nm, 480 nm to 490 nm, 485 nm to 495 nm, 490 nm to 500 nm, 500 nm to 550 nm, 525 nm to 575 nm, 550 nm to 600 nm, 575 nm to 625 nm, 600 nm to 650 nm, 625 nm to 675 nm, 650 nm to 700 nm, 675 nm to 725 nm, 700 nm to 750 nm, 725 nm to 775 nm, 750 nm to 800 nm, 775 nm to 825 nm, 800 nm to 850 nm, 825 nm to 875 nm, 850 nm to 900 nm, 925 nm to 975 nm, or 950 nm to 1000 nm. In some embodiments, the produced nanofiber structure (e.g., nanofiber mat) has a maximum pore size as determined by bubble point test (i.e., as set forth in ASTM Designation F316-03, “Standard Test Methods for Pore Size Characteristic of Membrane Filters by Bubble Point and Mean Flow Pore Test”, as reapproved in 2011) of no more than 500 nm, 450 nm, 400 nm, 350 nm, 300 nm, 250 nm 200 nm, 150 nm, 100 nm, or 50 nm. In some embodiments, the produced nanofiber structure (e.g., nanofiber mat) has a maximum pore size as determined by bubble point test of 10 nm to 20 nm, 15 nm to 25 nm, 20 nm to 30 nm, 25 nm to 35 nm, 30 nm to 40 nm, 35 nm to 45 nm, 40 nm to 50 nm, 45 nm to 55 nm, 50 nm to 60 nm, 55 nm to 65 nm, 60 nm to 70 nm, 65 nm to 75 nm, 70 nm to 80 nm, 75 nm to 85 nm, 80 nm to 90 nm, 85 nm to 95 nm, 90 nm to 100 nm, 95 nm to 105 nm, 100 nm to 110 nm, 105 nm to 115 nm, 110 nm to 120 nm, 115 nm to 125 nm, 120 nm to 130 nm, 125 nm to 135 nm, 130 nm to 140 nm, 135 nm to 145 nm, 140 nm to 150 nm, 145 nm to 155 nm, 150 nm to 160 nm, 155 nm to 165 nm, 160 nm to 170 nm, 165 nm to 175 nm, 170 nm to 180 nm, 175 nm to 185 nm, 180 nm to 190 nm, 185 nm to 195 nm, 190 nm to 200 nm, 195 nm to 205 nm, 200 nm to 210 nm, 205 nm to 215 nm, 210 nm to 220 nm, 215 nm to 225 nm, 220 nm to 230 nm, 225 nm to 235 nm, 230 nm to 240 nm, 235 nm to 245 nm, 240 nm to 250 nm, 245 nm to 255 nm, 250 nm to 260 nm, 255 nm to 265 nm, 260 nm to 270 nm, 265 nm to 275 nm, 270 nm to 280 nm, 275 nm to 285 nm, 280 nm to 290 nm, 285 nm to 295 nm, 290 nm to 300 nm, 295 nm to 305 nm, 300 nm to 310 nm, 305 nm to 315 nm, 310 nm to 320 nm, 315 nm to 325 nm, 320 nm to 330 nm, 325 nm to 335 nm, 330 nm to 340 nm, 335 nm to 345 nm, 340 nm to 350 nm, 345 nm to 355 nm, 350 nm to 360 nm, 355 nm to 365 nm, 360 nm to 370 nm, 365 nm to 375 nm, 370 nm to 380 nm, 375 nm to 385 nm, 380 nm to 390 nm, 385 nm to 395 nm, 390 nm to 400 nm, 395 nm to 405 nm, 400 nm to 410 nm, 405 nm to 415 nm, 410 nm to 420 nm, 415 nm to 425 nm, 420 nm to 430 nm, 425 nm to 435 nm, 430 nm to 440 nm, 435 nm to 445 nm, 440 nm to 450 nm, 445 nm to 455 nm, 450 nm to 460 nm, 455 nm to 465 nm, 460 nm to 470 nm, 465 nm to 475 nm, 470 nm to 480 nm, 475 nm to 485 nm, 480 nm to 490 nm, 485 nm to 495 nm, or 490 nm to 500 nm. In some embodiments, the produced electrospun structure (e.g., electrospun mat) has a porosity of at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95%. In some embodiments, the porosity is 70% to 95%, 75% to 95%, 80% to 95%, 85% to 95%. or 90% to 95%.

In some embodiments, the produced electrospun structure (e.g., electrospun mat) has a basis weight of at least about 1 gsm. In some, the electrospun structure has a basis weight of at least about 4 gsm. In some, the electrospun structure has a basis weight of at least about 5 gsm. In some, the electrospun structure has a basis weight of at least about 6 gsm. In some, the electrospun structure has a basis weight of at least about 7 gsm. In some, the electrospun structure has a basis weight of at least about 8 gsm.

In some embodiments, the method provided herein generates a nanofiber mat having a thickness of at least 35 μm and is generated at a line speed rate of at least 0.3 m/min. In some embodiments, the method provided herein generates a nanofiber mat having a thickness of at least 35 μm and is generated at a line speed rate of at least 0.35 m/min. In some embodiments, the method provided herein generates a nanofiber mat having a thickness of at least 15 μm and is generated at a line speed rate of at least 0.8 m/min. In some embodiments, the method provided herein generates a nanofiber mat having a thickness of at least 15 μm and is generated at a line speed rate of at least 0.9 m/min. In some embodiments, the method provided herein generates a nanofiber mat having a thickness of at least 15 μm and is generated at a line speed rate of at least 0.95 m/min.

In some embodiments, the method provided herein generates a nanofiber mat having a basis weight of at least 4.5 gsm and is generated at a line speed of at least 0.35 m/min. In some embodiments, the method provided herein generates a nanofiber mat having a basis weight of at least 2.4 gsm and is generated at a line speed of at least 0.60 m/min. In some embodiments, the method provided herein generates a nanofiber mat having a basis weight of at least 4.0 gsm and is generated at a line speed of at least 0.5 m/min. In some embodiments, the method provided herein generates a nanofiber mat having a basis weight of at least 2.3 gsm and is generated at a line speed of at least 0.9 m/min.

In some embodiments, the methods provided herein have a line speed of about 0.1 m/min, a ratio of the substrate distance to the interelectrode distance of about 0.25 to about 0.35, an electric field of about 0.57 kV/mm, and the produced electrospun mat has an average fiber diameter of about 100 nm to about 200 nm, and a basis weight of at least about 1.5 gsm, at least about 1.75 gsm, or at least about 2.0 gsm.

In some embodiments, the methods provided herein have a line speed of about 0.1 m/min, a ratio of the substrate distance to the interelectrode distance of about 0.45 to about 0.55, an electric field of about 0.7 kV/mm, and the produced electrospun mat has an average fiber diameter of about 100 nm to about 200 nm and a basis weight of at least about 3.1 gsm, at least about 3.2 gsm, or at least about 3.3 gsm.

In some embodiments, the nanofiber mat (e.g., a nanofiber mat having a fiber diameter of no more than 200 nm) is generated with a productivity of above at least 0.20 g/(m-min), above at least 0.21 g/(m-min), above at least 0.22 g/(m-min), above at least 0.23 g/(m-min), above at least 0.24 g/(m-min), above at least 0.25 g/(m-min), above at least 0.26 g/(m-min), above at least 0.27 g/(m-min), above at least 0.28 g/(m-min), above at least 0.29 g/(m-min), above at least 0.30 g/(m-min), above at least 0.31 g/(m-min), above at least 0.32 g/(m-min), or above at least 0.33 g/(m-min). In some embodiments, the nanofiber mat is produced with a productivity that is at least 5%, 10%, 15%, 20%, 25%, 30%, 30%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% higher than it would have been under identical conditions except that the ratio of the distance between the spinning electrode and the substrate (the substrate distance) to the distance between the spinning electrode and the collecting electrode (the interelectrode distance) been 1. In some embodiments, the nanofiber mat is produced with a productivity that is at least 5%, 10%, 15%, 20%, 25%, 30%, 30%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% higher than it would have been under identical conditions except that the ratio of the distance between the spinning electrode and the substrate (the substrate distance) to the distance between the spinning electrode and the collecting electrode (the interelectrode distance) been 0.88.

In some embodiments, the generated nanofiber mat has a fiber diameter variation of no more than 30%, no more than 29%, no more than 28%, no more than 27%, no more than 26%, no more than 25%, no more than 24%, no more than 23%, no more than 22%, no more than 21%, no more than 20%, no more than 19%, no more than 18%, no more than 17%.

In some embodiments, the nanofiber mat has a fiber diameter variation that is within 5%, 10%, 15%, or 20%, of what it would have been under identical conditions except that the ratio of the distance between the spinning electrode and the substrate (the substrate distance) to the distance between the spinning electrode and the collecting electrode (the interelectrode distance) been 1. In some embodiments, the nanofiber mat has a fiber diameter variation that is within 5%, 10%, 15%, or 20%, of what it would have been under identical conditions except that the ratio of the distance between the spinning electrode and the substrate (the substrate distance) to the distance between the spinning electrode and the collecting electrode (the interelectrode distance) been 0.88.

Test Methods

When reported herein, basis weight is determined according to ASTM procedure D-3776 /D3776M -09a (2017), “Standard Test Methods for Mass Per Unit Area (Weight) of Fabric,” and reported in g/m². When reported herein, porosity is calculated by dividing the basis weight of the sample in g/m² by the polymer density in g/cm³, by the sample thickness in micrometers, multiplying by 100, and subtracting the resulting number from 100, i.e., porosity=100−[basis weight/(density×thickness)×100].

When reported herein, fiber diameter is determined as follows: A scanning electron microscope (SEM) image was taken at (e.g., at 20,000, 40,000 or 60,000 times magnification) of each side of nanofiber mat sample. The diameter of at least ten (10) clearly distinguishable nanofibers are measured from each SEM image and recorded. Irregularities were not included (i.e., lumps of nanofibers, polymer drops, intersections of nanofibers, etc.). The average fiber diameter for both sides of each sample is calculated and averaged to result in a single average fiber diameter value for each sample.

When reported herein, nanofiber mat thickness is determined according to ASTM procedure 01777-96, “Standard Test Method for Thickness of Textile Materials,” and is reported in nanometers (nm) or micrometers (μm).

Productivity is calculated as the product of the basis weight (g/m²) and line speed (m/min) and is directly related to the process economy. In embodiments where there are more than one spinning electrode, productivity is normalized on a per-electrode basis (i.e., total productivity divided by the number of electrodes).

When reported herein, maximum pore size is determined by bubble point test as set forth in ASTM Designation F316-03, “Standard Test Methods for Pore Size Characteristic of Membrane Filters by Bubble Point and Mean Flow Pore Test”, as reapproved in 2011, and is reported in nanometers (nm).

When reported herein, substrate distance is the shortest distance between the substrate and the spinning electrode. When reported herein, inter electrode distance is the shortest distance between the spinning electrode and the collecting electrode. Such distances can be measured using any method known in the art (e.g., using measuring tape).

EXEMPLIFICATION EXAMPLE 1

A study was conducted to better understand how manipulating substrate distance and electric field affects spinning solution productivity during electrospinning processes. A half fraction factorial experiment was designed around substrate distance, voltage, and electric field. The FIG. 1 and FIG. 5 (rows 1-4) show the parameters for each of four experiments.

The electrospinning solution was prepared by dissolving Nylon 6,6 obtained from Sigma Aldrich in a mixture of three parts formic acid and one-part acetic acid at 80° C. for five hours.

Samples were produced on a modified NS 351000U electrospinning apparatus (Elmarco s.r.o. Liberec. CZ) retrofitted with a 50 cm long, 1-wire spinning electrode. On this instrument, samples were produced continuously in a roll to roll fashion in which the substrate moved over spinning electrodes at a constant speed. Samples were spun at 21 ° C. temperature, 4° C. dew point and 0.1 m/min line speed. BPM 85 Paper from Branopac, GmbH was used as a substrate on which the Nylon 6,6 nanofibers were collected. The solution was spun with nominal voltage of 80 kV and 100 kV, and electric field of 0.57 kV/mm and 0.70 kV/mm at substrate distances of 140 mm and 55 mm for 30 minutes. The electrospun nanofiber mats were then characterized to determine their basis weight (BW), thickness and fiber diameter.

An electrospinning mix was spun at an electric field of 0.57 kV/mm or 0.70 kV/mm and substrate distances of 140 mm or 55 mm. As shown in FIG. 2, a significant improvement in productivity observed at the shorter substrate distances and stronger electric fields. The best productivity improvement was realized while operating at the highest possible electric field and the lowest possible substrate distance. While further increase in electric field cause electrical arcing and interruption in the process, lowering substrate distance is the innate way to further improve fiber throughput.

Average fiber diameters of the mats produced under the experimental conditions tested are provided in FIG. 2. High electric field conditions resulted in statistically similar fiber diameters. Since, productivity can only be compared across similar fiber diameter, this further illustrates that the observed increase in basis weight at high productivity conditions has resulted from the increase in the mass of generated fibers.

EXAMPLE 2

Productivity improvement through the manipulation of substrate distance and electric field was further investigated (FIG. 5, rows 5-7). A 10.6 wt % Nylon 6,6 solution was prepared in 1 AA: 3 FA. This solution was electrospun using one pan and was collected on Branopac BPM85 paper at 0.094 m/min line speed. Samples were characterized for basis weight and fiber diameter. FIG. 3 shows a schematic of the electrospinning apparatus based on the parameters of (FIG. 5, rows 5-7).

Increasing the electric field resulted in a 1.7-fold increase in basis weight. Lowering substrate distance resulted in an additional 1.5-fold increase in basis weight. Overall a 2.6-fold increase was achieved by operating at higher electric fields and lower substrate distances. As shown in (FIG. 5, rows 5-7), the improvements observed in basis weights were not due to differences in fiber diameter.

Comparison of the results of experiment 7 to experiment 5 demonstrated that a productivity improvement can be realized through the production of a 2.6-fold higher basis weight sample at the same line speed. When experiment 3 is compared to experiment 5 it was demonstrated that the achieved productivity improvement can be realized to produce a similar basis weight sample at 2.5-fold higher line speeds.

EXAMPLE 3

A study was conducted to better understand how spinning solution productivity is affected by manipulating substrate distance while keeping the electric field approximately the same (FIG. 5, rows 8-11).

An electrospinning solution was prepared by dissolving 14% Nylon 6 obtained from BASF (Grade B17E) in a mixture of one-part formic acid and two-parts acetic acid at 80° C. for five hours. Samples were produced on a modified NS8S1600U electrospinning apparatus, (Elmarco s.r.o. Liberec. CZ). On this equipment, samples were produced continuously in a roll to roll fashion where the substrate moves over spinning electrodes at a constant speed. All samples were spun at 22 ° C. temperature, 4° C. dew point. Reemay 6125 nonwoven, commercially available from Berry Global (Waynesboro, Va.) was used as a substrate on which Nylon 6 nanofibers were collected. FIG. 5 (rows 8-11) summarizes the results of these conditions.

FIG. 4 provides a schematic of two sets of process settings used on above mentioned equipment to electrospun fibers. The first set of process settings consisted of nominal voltage of 100 kV, electric field of 0.49 kV/mm and substrate distance of 180 mm.

The samples were collected at line speeds of 0.35 and 0.54 m/min. The second set of process settings consisted of nominal voltage of 104 kV, electric field of 0.51 kV/mm and substrate distance of 155 mm. The samples were collected at line speeds ranging 0.35-0.98 m/min. The electrospun nanofiber mats were then characterized to determine their basis weight (BW), thickness and fiber diameter. FIG. 5 (rows 8-11) summarizes the process settings used and the properties of the membranes produced.

Comparison of the results obtained in experiment 8 and with those obtained in experiment 10 demonstrated ability to achieve the same membrane properties (basis weight, thickness, and fiber diameter) at a 1.4-fold faster line speed, just by lowering the substrate distance to interelectrode distance ratio. Similarly, comparing the results of experiment 9 and experiment 11 (FIG. 5) demonstrated ability to achieve the same membrane properties (basis weight, thickness, and fiber diameter) at 1.5-fold faster line speed by lowering the substrate distance to interelectrode distance ratio. Faster line speed represents higher productivity. Specifically, the increase in productivity was possible, even by keeping electric field approximately the same, by reducing the substrate distance, or ratio of substrate distance to interelectrode distance from 0.9 to 0.8.

The results of experiments 1-11 are summarized in the table provided in FIG. 5. FIG. 6 (a and b) is used to further illustrate the merit of decreasing the inter electrode distance (d-s/d-ie). FIG. 6, panel-a shows productivity in the scatter plot. FIG. 6, panel-b shows the fiber diameter measured using SEM. The higher productivity settings are marked by hatched bar graph. The run order is rearranged to deconvolute the effect of electrical field from substrate distance. For example, experimental runs [1,2] have electric field on 0.57 kV/mm, [4,3] have 0.7 kV/mm, [6,7] have 0.7 kV/mm. Production unit runs, [8-11] have electric fields that are marginally different and ranging 0.49-0.51 kV/mm. Thus, the comparison is primarily based on the distance ratio.

The fiber diameters for all settings are consistent and within measurement accuracy which permit comparing productivities, across different settings (FIG. 6, panel-a). FIG. 7 shows Scanning Electron Microscope (SEM) images of the electrospun nanofiber generated at (a) standard conditions in experiment 9 and (b) high productivity settings in experiment 10. The micrograph shows comparable fiber structures were obtained at both settings.

FIG. 6 (Exp # 1, 2 and 4,3) shows that 1.6 fold and 1.1 fold increase in productivity was achieved at electric field of 0.57 and 0.7 kV/mm, respectively. Similarly,

FIG. 6, panel-b (Exp# 6 and 7) shows another example of productivity improvement, particularly at a lower substrate speed (0.04 m/min), where 1.6 fold increase was observed even at high electric field of 0.7 kV/mm.

In many systems, electric field of 0.7 kV/mm is practically the upper cut-off of the electric field. Thus, additional increase in fiber production by manipulating the distance ratio is an advantage of this technique.

For the production unit, (Exp# 8-11) shows two examples where 1.4 fold - 1.5 fold increase in productivity was observed by lowering the inter electrode distance even if the electrical field was marginally increased from 0.49 to 0.51 kV/mm. For many production systems, operating above 0.51 kV/mm has safety and operational concerns.

Incorporation by Reference

All publications, patents, and patent applications mentioned herein are hereby incorporated by reference in their entirety as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference. In case of conflict, the present application, including any definitions herein, will control.

Equivalents

Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments described herein. Such equivalents are intended to be encompassed by the following claims. 

We claim:
 1. An electrospinning apparatus comprising: (a) a spinning electrode; (b) a substrate that is a first distance from the spinning electrode (the substrate distance); and (c) a collecting electrode that is a second distance from the spinning electrode (the interelectrode distance), wherein the substrate is positioned between the spinning electrode and the collecting electrode and wherein the ratio of the substrate distance to the interelectrode distance is less than 0.88.
 2. The electrospinning apparatus of claim 1, wherein the ratio of the substrate distance to the interelectrode is from about 0.86 to about 0.3.
 3. (canceled)
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 5. (canceled)
 6. (canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled)
 11. (canceled)
 12. (canceled)
 13. The electrospinning apparatus of claim 1, wherein the substrate distance to the spinning electrode is from about 180 mm to about 55 mm.
 14. The electrospinning apparatus of claim 1, wherein the interelectrode distance is such that the electrospinning apparatus maintains an electric field of 0.2 kV/mm to 0.8 kV/mm.
 15. (canceled)
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 17. (canceled)
 18. (canceled)
 19. (canceled)
 20. (canceled)
 21. The electrospinning apparatus of claim 1, wherein the substrate is a nonwoven fiber substrate, a non-porous film substrate, a membrane, paper or a porous substrate.
 22. The electrospinning apparatus of claim 1, wherein the spinning electrode further comprises a nozzle.
 23. The electrospinning apparatus of claim 1, wherein the spinning electrode is nozzleless.
 24. The electrospinning apparatus of claim 23, wherein the spinning electrode comprises a rotating roller or rotating drum or wire.
 25. The electrospinning apparatus of claim 1, wherein the collecting electrode comprises a conductive surface.
 26. The electrospinning apparatus of claim 25, wherein the collecting electrode is a flat plate, moving plate or belt, tube, wire, or rotating drum.
 27. The electrospinning apparatus of claim 1, wherein the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of 37 μmat at a rate of 0.35 m/min.
 28. The electrospinning apparatus of claim 1, wherein the electrospinning apparatus is capable of generating a nanofiber mat having a thickness of 19 μmat at a rate of 0.98 m/min.
 29. The electrospinning apparatus of claim 1, wherein the electrospinning apparatus is capable of generating a nanofiber mat having a fiber diameter of no more than 200 nm and a basis weight of at least about 1.2 gsm at line speed of at least 0.04 m/min.
 30. The electrospinning apparatus of claim 1, wherein the electrospinning apparatus is capable of generating a nanofiber mat having a fiber diameter of no more than 200 nm with a productivity of above at least 0.20 g/(m-min).
 31. (canceled)
 32. (canceled)
 33. (canceled)
 34. (canceled)
 35. The electrospinning apparatus of claim 1, wherein the electrospinning apparatus is capable of generating a nanofiber mat having a fiber diameter variation of no more than 36%.
 36. (canceled)
 37. (canceled)
 38. (canceled)
 39. An electrospinning apparatus comprising: (a) a spinning electrode; (b) a substrate that is a first distance from the spinning electrode (the substrate distance); and (c) a collecting electrode that is a second distance from the spinning electrode (the interelectrode distance), wherein the apparatus is configured such that the substrate distance and the interelectrode distance are separately adjustable and capable of being configured such that the ratio of the substrate distance to the interelectrode distance is no greater than 0.77.
 40. The electrospinning apparatus of claim 39, wherein the substrate distance can be adjusted without adjusting the interelectrode distance.
 41. The electrospinning apparatus of claim 39, wherein the substrate distance can be adjusted using a knob, lever, button or motor.
 42. (canceled)
 43. The electrospinning apparatus of claim 39, wherein the substrate is a nonwoven fiber substrate, non-porous film substrate, or porous substrate.
 44. The electrospinning apparatus of claim 39, wherein the spinning electrode further comprises a nozzle.
 45. The electrospinning apparatus of claim 39, wherein the spinning electrode is nozzleless.
 46. The electrospinning apparatus of claim 39, wherein the spinning electrode comprises a rotating roller or rotating drum or wire.
 47. The electrospinning apparatus of claim 39, wherein the collecting electrode comprises a conductive surface.
 48. The electrospinning apparatus of claim 47, wherein the collecting electrode is a flat plate, moving plate, tube, wire, or rotating drum.
 49. (canceled)
 50. A method for producing a nanofiber mat comprising electrospinning a polymer solution from a spinning electrode onto a substrate that is positioned between the spinning electrode and a collecting electrode, wherein the ratio of the distance between the spinning electrode and the substrate (the substrate distance) to the distance between the spinning electrode and the collecting electrode (the interelectrode distance) is less than 0.88.
 51. The method of claim 50, wherein the ratio of the distance between the spinning electrode and the substrate (the substrate distance) to the distance between the spinning electrode and the collecting electrode (the interelectrode distance) is less than 0.9, less than 0.8, less than 0.7, less than 0.6, less than 0.5, less than 0.4 or less than 0.3.
 52. (canceled)
 53. (canceled)
 54. (canceled)
 55. (canceled)
 56. (canceled)
 57. (canceled)
 58. The method of claim 50, wherein the nanofibers are electrospun at a total applied voltage across both electrodes between 10 kV to 500 kV, 50 kV to 450 kV, 100 kV to 400 kV, 150 kV to 350 kV, or 200 kV to 300 kV.
 59. The method of claim 50, wherein the nanofibers are electrospun in an electric field of 0.2 kV/mm to 0.8 kV/mm.
 60. (canceled)
 61. (canceled)
 62. (canceled)
 63. (canceled)
 64. (canceled)
 65. (canceled)
 66. (canceled)
 67. The method of claim 50, wherein the substrate is a nonwoven fiber substrate, a non-porous film substrate, paper or a porous substrate.
 68. The method of claim 50, wherein the electrospinning is needle-electrospinning.
 69. The method of claim 50, wherein the electrospinning is needleless-electrospinning.
 70. The method of claim 50, wherein the collecting electrode comprises a conductive surface.
 71. The method of claim 70, wherein the collecting electrode is a flat plate, moving plate, tube, wire, or rotating drum.
 72. The method of claim 50, wherein the nanofiber mat has a thickness from about 1 μm to about 500 μm.
 73. The method of claim 50, wherein the nanofiber mat has an average fiber diameter from about 10 nm to about 1000 nm.
 74. The method of claim 50, wherein the nanofiber mat has a maximum pore size as determined by bubble point test of no more than 500 nm.
 75. The method of claim 50, wherein the nanofiber mat has a fiber diameter of no more than 200 nm and is produced with a productivity of above at least 0.20 g/(m-min).
 76. (canceled)
 77. (canceled)
 78. (canceled)
 79. (canceled)
 80. The method of claim 50, wherein the nanofiber mat has a fiber diameter of no more than 200 nm and is produced with a productivity that is at least 5% to 50% higher than it would have been under identical conditions except that the ratio of the distance between the spinning electrode and the substrate (the substrate distance) to the distance between the spinning electrode and the collecting electrode (the interelectrode distance) been
 1. 81. (canceled)
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 85. (canceled)
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 87. (canceled)
 88. The method of any one of claim 50, wherein, wherein the nanofiber mat has a fiber diameter variation of no more than 36%.
 89. (canceled)
 90. (canceled)
 91. (canceled).
 92. (canceled)
 93. (canceled)
 94. The method of claim 50, wherein the polymer solution comprises a polymer or a polymer blend.
 95. The method of claim 94, wherein the polymer or polymer blend is selected from nylon-6, nylon-46, nylon-66, polyurethane (PU), polybenzimidazole, polycarbonate, polyacrylonitrile, polyvinyl alcohol, polylactic acid (PLA), polyethylene-co-vinyl acetate (PEVA), PEVA/PLA, polymethylmethacrylate (PMMA), PMMA/tetrahydroperfluorooctylacrylate (TAN), polyethylene oxide (PEO), collagen-PEO, polystyrene (PS), polyaniline (PANI)/PEO, PANI/PS, polyvinylcarbazole, polyethylene terephthalate (PET), polyacrylic acid-polypyrene methanol (PAA-PM), polyamide (PA), silk/PEO, polyvinylphenol (PVP), polyvinylchloride (PVC), cellulose acetate (CA), PAA- PM/PU, polyvinyl alcohol (PVA)/silica, polyacrylamide (PAAm), poly(lactic-co-glycolic acid) (PLGA), polycarprolactone (PCL), poly(2-hydroxyethyl methacrylate) (HEMA), poly(vinylidene difluoride) (PVDF), PVDF/PMMA, polyether imide (PEI), polyethylene glycol (PEG), poy(ferrocenyldimethylsilane) (PFDMS), Nylon6/montmorillonite (Mt), poly(ethylene-co-vinyl alcohol), polyacrylnitrile (PAN)/TiO2, polycaprolactone (PCL)/metal, polyvinyl porrolidone, polymetha-phenylene isophthalamide, polyethylene (PE), polypropylene (PP), nylon-12, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), polyvinyl butyral (PVB), PET/PEN, or a blend thereof.
 96. The method of any one of claim 50, wherein the nanofiber mat is generated at a line speed of 0.03 m/min to 1 m/min.
 97. The method of claim 96, wherein the line speed is about 0.04 m/min.
 98. The method of claim 97, wherein the ratio of the substrate distance to the interelectrode distance is about 0.45 to about 0.55.
 99. The method of claim 98, wherein the nanofiber mat is electrospun in an electric field of about 0.7 kV/mm.
 100. The method of claim 99, wherein the electrospun mat has an average fiber diameter of about 100 nm to about 200 nm.
 101. The method of claim 100, wherein the electrospun mat has a basis weight of at least about 6 to about 8 gsm.
 102. (canceled)
 103. (canceled)
 104. The method of claim 96, wherein the line speed is about 0.1 m/min
 105. The method of claim 104, wherein the ratio of the substrate distance to the interelectrode distance is about 0.25 to about 0.35.
 106. The method of claim 105, wherein the nanofiber mat is electrospun in an electric field of about 0.57 kV/mm.
 107. The method of claim 106, wherein the electrospun mat has an average fiber diameter of about 100 nm to about 200 nm.
 108. The method of claim 107, wherein the electrospun mat has a basis weight of at least about 1.5 gsm to about 2.0 gsm.
 109. (canceled)
 110. (canceled)
 111. The method of claim 104, wherein the ratio of the substrate distance to the interelectrode distance is about 0.45 to about 0.55.
 112. The method of claim 111, wherein the nanofiber mat is electrospun in an electric field of about 0.7 kV/mm.
 113. The method of claim 112, wherein the electrospun mat has an average fiber diameter of about 100 nm to about 200 nm.
 114. The method of claim 113, wherein the electrospun mat has a basis weight of at least about 3.1 gsm to about 3.3 GSM.
 115. (canceled)
 116. (canceled)
 117. The method of claim 50, wherein the nanofiber mat has a thickness of at least 35 μm and is generated at a line speed rate of at least 0.3 m/min.
 118. (canceled)
 119. The method of any one of claim 50, wherein the nanofiber mat has a thickness of at least 15 μm and is generated at a line speed rate of at least 0.8 m/min to at least 0.95 m/min.
 120. (canceled)
 121. (canceled)
 122. The method of claim 50, wherein the nanofiber mat has a basis weight of at least 4.5 gsm and is generated at a line speed of at least 0.35 m/min.
 123. (canceled)
 124. (canceled)
 125. (canceled) 